In the automotive industry, engine friction and wear reduction by adding additives to an oil-based lubricant is one of the most appealing approaches for improving vehicle fuel economy. This is because the benefits potentially realizable can be readily applied to all vehicles at low cost. Additives have been added to oil-based lubricants to reduce friction and wear by creating chemical reactions between the additives and the metal surfaces. However, these chemical reactions are very slow and the reaction films thus formed are generally not uniform. It has also been proposed that metal surfaces may be coated with friction-reducing or wear-reducing films before they are assembled into a vehicle. However, it is extremely difficult to repair damaged friction-reducing or wear-reducing films after a vehicle has been assembled and operated.
The formation of friction-reducing and wear-reducing films on metal surfaces immersed in aqueous solutions or molten salts by an electrochemical technique has been performed by others. Great difficulties were encountered when the same electrochemical technique was used in a process to form friction-reducing and wear-reducing films on metal surfaces immersed in oil-based lubricants. Since oil-based lubricants have extremely high electrical resistance, electrical current cannot pass through the lubricants.
It is therefore an object of the present invention to provide a method of coating metal surfaces immersed in oil-based lubricants with a friction-reducing and wear-reducing film by an electrochemical process.
It is another object of the present invention to provide a method of coating metal surfaces immersed in oil-based lubricants with a friction-reducing and wear-reducing film electrochemically by adding an additive to the oil-based lubricant such that electrical current may pass between the two metal surfaces immersed in the oil-based lubricant.
It is a further object of the present invention to provide a method of coating metal surfaces immersed in oil-based lubricants with a friction-reducing and wear-reducing film electrochemically by adding a dialkyl hydrogen phosphate additive to the lubricant such that the friction and wear properties of the metal surfaces are improved.